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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::unordered_map&lt;Key,T,Hash,KeyEqual,Allocator&gt;::</span>unordered_map</h1>
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<tr class="t-nv-h1"><td colspan="5">成员函数</td></tr>
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<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="begin.html" title="cpp/container/unordered map/begin"><span class="t-lines"><span>unordered_map::begin</span><span>unordered_map::cbegin</span></span></a></div></div></td></tr>
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<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="empty.html" title="cpp/container/unordered map/empty"><span class="t-lines"><span>unordered_map::empty</span></span></a></div></div></td></tr>
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<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="clear.html" title="cpp/container/unordered map/clear"><span class="t-lines"><span>unordered_map::clear</span></span></a></div></div></td></tr>
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<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="insert_or_assign.html" title="cpp/container/unordered map/insert or assign"><span class="t-lines"><span>unordered_map::insert_or_assign</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span></span></div></div></td></tr>
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<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="merge.html" title="cpp/container/unordered map/merge"><span class="t-lines"><span>unordered_map::merge</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span></span></div></div></td></tr>
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<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="at.html" title="cpp/container/unordered map/at"><span class="t-lines"><span>unordered_map::at</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="operator_at.html" title="cpp/container/unordered map/operator at"><span class="t-lines"><span>unordered_map::operator[]</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="count.html" title="cpp/container/unordered map/count"><span class="t-lines"><span>unordered_map::count</span></span></a></div></div></td></tr>
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<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="equal_range.html" title="cpp/container/unordered map/equal range"><span class="t-lines"><span>unordered_map::equal_range</span></span></a></div></div></td></tr>
<tr class="t-nv-h2"><td colspan="5">桶接口</td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="begin2.html" title="cpp/container/unordered map/begin2"><span class="t-lines"><span>unordered_map::begin<span class="t-dsc-small">(size_type)</span></span><span>unordered_map::cbegin<span class="t-dsc-small">(size_type)</span></span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="end2.html" title="cpp/container/unordered map/end2"><span class="t-lines"><span>unordered_map::end<span class="t-dsc-small">(size_type)</span></span><span>unordered_map::cend<span class="t-dsc-small">(size_type)</span></span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="bucket_count.html" title="cpp/container/unordered map/bucket count"><span class="t-lines"><span>unordered_map::bucket_count</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="max_bucket_count.html" title="cpp/container/unordered map/max bucket count"><span class="t-lines"><span>unordered_map::max_bucket_count</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="bucket_size.html" title="cpp/container/unordered map/bucket size"><span class="t-lines"><span>unordered_map::bucket_size</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="bucket.html" title="cpp/container/unordered map/bucket"><span class="t-lines"><span>unordered_map::bucket</span></span></a></div></div></td></tr>
<tr class="t-nv-h2"><td colspan="5">哈希策略</td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="load_factor.html" title="cpp/container/unordered map/load factor"><span class="t-lines"><span>unordered_map::load_factor</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="max_load_factor.html" title="cpp/container/unordered map/max load factor"><span class="t-lines"><span>unordered_map::max_load_factor</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="rehash.html" title="cpp/container/unordered map/rehash"><span class="t-lines"><span>unordered_map::rehash</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="reserve.html" title="cpp/container/unordered map/reserve"><span class="t-lines"><span>unordered_map::reserve</span></span></a></div></div></td></tr>
<tr class="t-nv-h2"><td colspan="5">观察器</td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="hash_function.html" title="cpp/container/unordered map/hash function"><span class="t-lines"><span>unordered_map::hash_function</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="key_eq.html" title="cpp/container/unordered map/key eq"><span class="t-lines"><span>unordered_map::key_eq</span></span></a></div></div></td></tr>
<tr class="t-nv-h1"><td colspan="5">非成员函数</td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="operator_cmp.html" title="cpp/container/unordered map/operator cmp"><span class="t-lines"><span>operator==</span><span>operator!=</span></span></a></div><div><span class="t-lines"><span></span><span><span class="t-mark-rev t-until-cxx20">(C++20 前)</span></span></span></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="swap2.html" title="cpp/container/unordered map/swap2"><span class="t-lines"><span>std::swap</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="erase_if.html" title="cpp/container/unordered map/erase if"><span class="t-lines"><span>erase_if</span></span></a></div><div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div></div></td></tr>
<tr class="t-nv-h1"><td colspan="5"> <a href="deduction_guides.html" title="cpp/container/unordered map/deduction guides">推导指引</a><span class="t-mark-rev t-since-cxx17">(C++17)</span></td></tr>
</table></div><div></div></div></div></div><div class="t-navbar-sep"> </div></div>
<table class="t-dcl-begin"><tbody>
<tr class="t-dcl t-since-cxx11">
<td> <div><span class="mw-geshi cpp source-cpp">unordered_map<span class="br0">(</span><span class="br0">)</span> <span class="sy4">:</span> unordered_map<span class="br0">(</span> size_type<span class="br0">(</span><span class="coMULTI">/*implementation-defined*/</span><span class="br0">)</span> <span class="br0">)</span> <span class="br0">{</span><span class="br0">}</span><br>
<p><span class="kw1">explicit</span> unordered_map<span class="br0">(</span> size_type bucket_count,<br>
                        <span class="kw4">const</span> Hash<span class="sy3">&amp;</span> hash <span class="sy1">=</span> Hash<span class="br0">(</span><span class="br0">)</span>,<br>
                        <span class="kw4">const</span> key_equal<span class="sy3">&amp;</span> equal <span class="sy1">=</span> key_equal<span class="br0">(</span><span class="br0">)</span>,<br>
</p>
                        <span class="kw4">const</span> Allocator<span class="sy3">&amp;</span> alloc <span class="sy1">=</span> Allocator<span class="br0">(</span><span class="br0">)</span> <span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td> (1) </td>
<td> <span class="t-mark-rev t-since-cxx11">(C++11 起)</span> </td>
</tr>
<tr class="t-dcl t-since-cxx14">
<td> <div><span class="mw-geshi cpp source-cpp">unordered_map<span class="br0">(</span> size_type bucket_count,<br>
<p>               <span class="kw4">const</span> Allocator<span class="sy3">&amp;</span> alloc <span class="br0">)</span><br>
              <span class="sy4">:</span> unordered_map<span class="br0">(</span>bucket_count, Hash<span class="br0">(</span><span class="br0">)</span>, key_equal<span class="br0">(</span><span class="br0">)</span>, alloc<span class="br0">)</span> <span class="br0">{</span><span class="br0">}</span><br>
unordered_map<span class="br0">(</span> size_type bucket_count,<br>
               <span class="kw4">const</span> Hash<span class="sy3">&amp;</span> hash,<br>
               <span class="kw4">const</span> Allocator<span class="sy3">&amp;</span> alloc <span class="br0">)</span><br>
</p>
              <span class="sy4">:</span> unordered_map<span class="br0">(</span>bucket_count, hash, key_equal<span class="br0">(</span><span class="br0">)</span>, alloc<span class="br0">)</span> <span class="br0">{</span><span class="br0">}</span></span></div></td>
<td> (1) </td>
<td> <span class="t-mark-rev t-since-cxx14">(C++14 起)</span> </td>
</tr>
<tr class="t-dcl t-since-cxx11">
<td> <div><span class="mw-geshi cpp source-cpp"><span class="kw1">explicit</span> unordered_map<span class="br0">(</span> <span class="kw4">const</span> Allocator<span class="sy3">&amp;</span> alloc <span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td> (1) </td>
<td> <span class="t-mark-rev t-since-cxx11">(C++11 起)</span> </td>
</tr>
<tr class="t-dcl t-since-cxx11">
<td> <div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1">&lt;</span> <span class="kw1">class</span> InputIt <span class="sy1">&gt;</span><br>
<p>unordered_map<span class="br0">(</span> InputIt first, InputIt last,<br>
               size_type bucket_count <span class="sy1">=</span> <span class="coMULTI">/*implementation-defined*/</span>,<br>
               <span class="kw4">const</span> Hash<span class="sy3">&amp;</span> hash <span class="sy1">=</span> Hash<span class="br0">(</span><span class="br0">)</span>,<br>
               <span class="kw4">const</span> key_equal<span class="sy3">&amp;</span> equal <span class="sy1">=</span> key_equal<span class="br0">(</span><span class="br0">)</span>,<br>
</p>
               <span class="kw4">const</span> Allocator<span class="sy3">&amp;</span> alloc <span class="sy1">=</span> Allocator<span class="br0">(</span><span class="br0">)</span> <span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td> (2) </td>
<td> <span class="t-mark-rev t-since-cxx11">(C++11 起)</span> </td>
</tr>
<tr class="t-dcl t-since-cxx14">
<td> <div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1">&lt;</span> <span class="kw1">class</span> InputIt <span class="sy1">&gt;</span><br>
<p>unordered_map<span class="br0">(</span> InputIt first, InputIt last,<br>
               size_type bucket_count,<br>
               <span class="kw4">const</span> Allocator<span class="sy3">&amp;</span> alloc <span class="br0">)</span><br>
              <span class="sy4">:</span> unordered_map<span class="br0">(</span>first, last, <br>
</p>
                  bucket_count, Hash<span class="br0">(</span><span class="br0">)</span>, key_equal<span class="br0">(</span><span class="br0">)</span>, alloc<span class="br0">)</span> <span class="br0">{</span><span class="br0">}</span></span></div></td>
<td> (2) </td>
<td> <span class="t-mark-rev t-since-cxx14">(C++14 起)</span> </td>
</tr>
<tr class="t-dcl t-since-cxx14">
<td> <div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1">&lt;</span> <span class="kw1">class</span> InputIt <span class="sy1">&gt;</span><br>
<p>unordered_map<span class="br0">(</span> InputIt first, InputIt last,<br>
               size_type bucket_count,<br>
               <span class="kw4">const</span> Hash<span class="sy3">&amp;</span> hash,<br>
               <span class="kw4">const</span> Allocator<span class="sy3">&amp;</span> alloc <span class="br0">)</span> <br>
              <span class="sy4">:</span> unordered_map<span class="br0">(</span>first, last, <br>
</p>
                  bucket_count, hash, key_equal<span class="br0">(</span><span class="br0">)</span>, alloc<span class="br0">)</span> <span class="br0">{</span><span class="br0">}</span></span></div></td>
<td> (2) </td>
<td> <span class="t-mark-rev t-since-cxx14">(C++14 起)</span> </td>
</tr>
<tr class="t-dcl t-since-cxx11">
<td> <div><span class="mw-geshi cpp source-cpp">unordered_map<span class="br0">(</span> <span class="kw4">const</span> unordered_map<span class="sy3">&amp;</span> other <span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td> (3) </td>
<td> <span class="t-mark-rev t-since-cxx11">(C++11 起)</span> </td>
</tr>
<tr class="t-dcl t-since-cxx11">
<td> <div><span class="mw-geshi cpp source-cpp">unordered_map<span class="br0">(</span> <span class="kw4">const</span> unordered_map<span class="sy3">&amp;</span> other, <span class="kw4">const</span> Allocator<span class="sy3">&amp;</span> alloc <span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td> (3) </td>
<td> <span class="t-mark-rev t-since-cxx11">(C++11 起)</span> </td>
</tr>
<tr class="t-dcl t-since-cxx11">
<td> <div><span class="mw-geshi cpp source-cpp">unordered_map<span class="br0">(</span> unordered_map<span class="sy3">&amp;&amp;</span> other <span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td> (4) </td>
<td> <span class="t-mark-rev t-since-cxx11">(C++11 起)</span> </td>
</tr>
<tr class="t-dcl t-since-cxx11">
<td> <div><span class="mw-geshi cpp source-cpp">unordered_map<span class="br0">(</span> unordered_map<span class="sy3">&amp;&amp;</span> other, <span class="kw4">const</span> Allocator<span class="sy3">&amp;</span> alloc <span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td> (4) </td>
<td> <span class="t-mark-rev t-since-cxx11">(C++11 起)</span> </td>
</tr>
<tr class="t-dcl t-since-cxx11">
<td> <div><span class="mw-geshi cpp source-cpp">unordered_map<span class="br0">(</span> <a href="../../utility/initializer_list.html"><span class="kw960">std::<span class="me2">initializer_list</span></span></a><span class="sy1">&lt;</span>value_type<span class="sy1">&gt;</span> init,<br>
<p>               size_type bucket_count <span class="sy1">=</span> <span class="coMULTI">/*implementation-defined*/</span>,<br>
               <span class="kw4">const</span> Hash<span class="sy3">&amp;</span> hash <span class="sy1">=</span> Hash<span class="br0">(</span><span class="br0">)</span>,<br>
               <span class="kw4">const</span> key_equal<span class="sy3">&amp;</span> equal <span class="sy1">=</span> key_equal<span class="br0">(</span><span class="br0">)</span>,<br>
</p>
               <span class="kw4">const</span> Allocator<span class="sy3">&amp;</span> alloc <span class="sy1">=</span> Allocator<span class="br0">(</span><span class="br0">)</span> <span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td> (5) </td>
<td> <span class="t-mark-rev t-since-cxx11">(C++11 起)</span> </td>
</tr>
<tr class="t-dcl t-since-cxx14">
<td> <div><span class="mw-geshi cpp source-cpp">unordered_map<span class="br0">(</span> <a href="../../utility/initializer_list.html"><span class="kw960">std::<span class="me2">initializer_list</span></span></a><span class="sy1">&lt;</span>value_type<span class="sy1">&gt;</span> init,<br>
<p>               size_type bucket_count,<br>
               <span class="kw4">const</span> Allocator<span class="sy3">&amp;</span> alloc <span class="br0">)</span> <br>
              <span class="sy4">:</span> unordered_map<span class="br0">(</span>init, bucket_count, <br>
</p>
                  Hash<span class="br0">(</span><span class="br0">)</span>, key_equal<span class="br0">(</span><span class="br0">)</span>, alloc<span class="br0">)</span> <span class="br0">{</span><span class="br0">}</span></span></div></td>
<td> (5) </td>
<td> <span class="t-mark-rev t-since-cxx14">(C++14 起)</span> </td>
</tr>
<tr class="t-dcl t-since-cxx14">
<td> <div><span class="mw-geshi cpp source-cpp">unordered_map<span class="br0">(</span> <a href="../../utility/initializer_list.html"><span class="kw960">std::<span class="me2">initializer_list</span></span></a><span class="sy1">&lt;</span>value_type<span class="sy1">&gt;</span> init,<br>
<p>               size_type bucket_count,<br>
               <span class="kw4">const</span> Hash<span class="sy3">&amp;</span> hash,<br>
               <span class="kw4">const</span> Allocator<span class="sy3">&amp;</span> alloc <span class="br0">)</span> <br>
              <span class="sy4">:</span> unordered_map<span class="br0">(</span>init, bucket_count, <br>
</p>
                  hash, key_equal<span class="br0">(</span><span class="br0">)</span>, alloc<span class="br0">)</span> <span class="br0">{</span><span class="br0">}</span></span></div></td>
<td> (5) </td>
<td> <span class="t-mark-rev t-since-cxx14">(C++14 起)</span> </td>
</tr>
<tr class="t-dcl-sep"><td></td><td></td><td></td></tr>
</tbody></table>
<p>从各种数据源构造新容器。可选的以用户提供的 <code>bucket_count</code> 为用于创建的最小桶数，以 <code>hash</code> 为哈希函数，以 <code>equal</code> 为比较关键的函数，和以 <code>alloc</code> 为分配器。
</p>
<div class="t-li1"><span class="t-li">1)</span> 构造空容器。设置 <code>max_load_factor()</code> 为 1.0 。对于默认构造函数，桶数是实现定义的。</div>
<div class="t-li1"><span class="t-li">2)</span> 构造拥有范围 <code>[first, last)</code> 的内容的容器。设置 <code>max_load_factor()</code> 为 1.0 。若范围中的多个元素拥有比较等价的关键，则插入哪个元素是未指定的（待决的 <a rel="nofollow" class="external text" href="http://wg21.link/lwg2844">LWG2844</a> ）。</div>
<div class="t-li1"><span class="t-li">3)</span> 复制构造函数。构造拥有 <code>other</code> 内容副本的容器，一同复制加载因子、谓词和哈希函数。若不提供 <code>alloc</code> ，则通过调用 <span class="t-c"><span class="mw-geshi cpp source-cpp"><a href="../../memory/allocator_traits.html"><span class="kw701">std::<span class="me2">allocator_traits</span></span></a><span class="sy1">&lt;</span>allocator_type<span class="sy1">&gt;</span><span class="sy4">::</span><span class="me2">select_on_container_copy_construction</span><span class="br0">(</span>other.<span class="me1">get_allocator</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span></span></span> 获得分配器。</div>
<div class="t-li1"><span class="t-li">4)</span> 移动构造函数。用移动语义构造拥有 <code>other</code> 内容的容器。若不提供 <code>alloc</code> ，则通过从属于 <code>other</code> 的分配器移动构造获得分配器。</div>
<div class="t-li1"><span class="t-li">5)</span> 构造拥有 initializer_list <code>init</code> 内容的容器，同 unordered_map(init.begin(), init.end()) 。</div>
<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
<table class="t-par-begin">


<tr class="t-par">
<td>  alloc
</td>
<td> -
</td>
<td> 用于此容器所有内存分配器的分配器
</td></tr>
<tr class="t-par">
<td>  bucket_count
</td>
<td> -
</td>
<td> 初始化时用的最小桶数。若不指定，则使用实现定义的默认值
</td></tr>
<tr class="t-par">
<td>  hash
</td>
<td> -
</td>
<td> 要用的哈希函数
</td></tr>
<tr class="t-par">
<td>  equal
</td>
<td> -
</td>
<td> 用于此容器所有关键比较的比较函数
</td></tr>
<tr class="t-par">
<td>  first, last
</td>
<td> -
</td>
<td> 复制元素来源的范围
</td></tr>
<tr class="t-par">
<td>  other
</td>
<td> -
</td>
<td> 用作源以初始化容器元素的另一容器
</td></tr>
<tr class="t-par">
<td>  init
</td>
<td> -
</td>
<td> 用以初始化容器元素的 initializer_list
</td></tr>
<tr class="t-par-hitem">
<td colspan="3"> 类型要求
</td></tr>
<tr class="t-par-req">
<td colspan="3"> -<div class="spacer"></div><code>InputIt</code> 必须满足<a href="../../named_req/InputIterator.html" title="cpp/named req/InputIterator"><i>遗留输入迭代器</i> <span style="font-family: Georgia, 'DejaVu Serif', serif; font-style:italic">(LegacyInputIterator)</span> </a> 的要求。
</td></tr></table>
<h3><span class="mw-headline" id=".E5.A4.8D.E6.9D.82.E5.BA.A6">复杂度</span></h3>
<div class="t-li1"><span class="t-li">1)</span> 常数</div>
<div class="t-li1"><span class="t-li">2)</span> 平均情况与 <code>first</code> 和 <code>last</code> 间的距离成线性，最坏情况成平方。</div>
<div class="t-li1"><span class="t-li">3)</span> 与 <code>other</code> 的大小成线性。</div>
<div class="t-li1"><span class="t-li">4)</span> 常数。若给定 <code>alloc</code> 且 <span class="t-c"><span class="mw-geshi cpp source-cpp">alloc <span class="sy3">!</span><span class="sy1">=</span> other.<span class="me1">get_allocator</span><span class="br0">(</span><span class="br0">)</span></span></span> 则为线性。</div>
<div class="t-li1"><span class="t-li">5)</span> 平均情况与 <code>init</code> 的大小成线性，最坏情况成平方。</div>
<h3><span class="mw-headline" id=".E5.BC.82.E5.B8.B8">异常</span></h3>
<p>对 <code>Allocator::allocate</code> 的调用可能抛出。
</p>
<h3><span class="mw-headline" id=".E6.B3.A8.E6.84.8F">注意</span></h3>
<div class="t-template-editlink" style="">
</div>在容器移动构造（重载 <span class="t-v">(4)</span> ）后，指向 <code>other</code> 的引用及迭代器（除了尾迭代器）保持合法，但指代现于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="sy2">*</span>this</span></span> 中的元素。当前标准由 <a rel="nofollow" class="external text" href="http://eel.is/c++draft/container.requirements.general#12">[container.requirements.general]/12</a> 中的总括陈述作出此保证，而 <a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue2321">LWG 2321</a> 正在考虑更严格的保证。
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
<div class="t-example"><div class="t-example-live-link"><div class="coliru-btn coliru-btn-run-init">运行此代码</div></div>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="co2">#include &lt;unordered_map&gt;</span>
<span class="co2">#include &lt;vector&gt;</span>
<span class="co2">#include &lt;bitset&gt;</span>
<span class="co2">#include &lt;string&gt;</span>
<span class="co2">#include &lt;utility&gt;</span>
 
<span class="kw1">struct</span> Key <span class="br0">{</span>
    <a href="../../string/basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> first<span class="sy4">;</span>
    <a href="../../string/basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a> second<span class="sy4">;</span>
<span class="br0">}</span><span class="sy4">;</span>
 
<span class="kw1">struct</span> KeyHash <span class="br0">{</span>
 <a href="../../types/size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> operator<span class="br0">(</span><span class="br0">)</span><span class="br0">(</span><span class="kw4">const</span> Key<span class="sy3">&amp;</span> k<span class="br0">)</span> <span class="kw4">const</span>
 <span class="br0">{</span>
     <span class="kw1">return</span> <a href="../../utility/hash.html"><span class="kw1124">std::<span class="me2">hash</span></span></a><span class="sy1">&lt;</span><a href="../../string/basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a><span class="sy1">&gt;</span><span class="br0">(</span><span class="br0">)</span><span class="br0">(</span>k.<span class="me1">first</span><span class="br0">)</span> <span class="sy3">^</span>
            <span class="br0">(</span><a href="../../utility/hash.html"><span class="kw1124">std::<span class="me2">hash</span></span></a><span class="sy1">&lt;</span><a href="../../string/basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a><span class="sy1">&gt;</span><span class="br0">(</span><span class="br0">)</span><span class="br0">(</span>k.<span class="me1">second</span><span class="br0">)</span> <span class="sy1">&lt;&lt;</span> <span class="nu0">1</span><span class="br0">)</span><span class="sy4">;</span>
 <span class="br0">}</span>
<span class="br0">}</span><span class="sy4">;</span>
 
<span class="kw1">struct</span> KeyEqual <span class="br0">{</span>
 <span class="kw4">bool</span> operator<span class="br0">(</span><span class="br0">)</span><span class="br0">(</span><span class="kw4">const</span> Key<span class="sy3">&amp;</span> lhs, <span class="kw4">const</span> Key<span class="sy3">&amp;</span> rhs<span class="br0">)</span> <span class="kw4">const</span>
 <span class="br0">{</span>
    <span class="kw1">return</span> lhs.<span class="me1">first</span> <span class="sy1">==</span> rhs.<span class="me1">first</span> <span class="sy3">&amp;&amp;</span> lhs.<span class="me1">second</span> <span class="sy1">==</span> rhs.<span class="me1">second</span><span class="sy4">;</span>
 <span class="br0">}</span>
<span class="br0">}</span><span class="sy4">;</span>
 
<span class="kw1">struct</span> Foo <span class="br0">{</span>
    Foo<span class="br0">(</span><span class="kw4">int</span> val_<span class="br0">)</span> <span class="sy4">:</span> val<span class="br0">(</span>val_<span class="br0">)</span> <span class="br0">{</span><span class="br0">}</span>
    <span class="kw4">int</span> val<span class="sy4">;</span>
    <span class="kw4">bool</span> operator<span class="sy1">==</span><span class="br0">(</span><span class="kw4">const</span> Foo <span class="sy3">&amp;</span>rhs<span class="br0">)</span> <span class="kw4">const</span> <span class="br0">{</span> <span class="kw1">return</span> val <span class="sy1">==</span> rhs.<span class="me1">val</span><span class="sy4">;</span> <span class="br0">}</span>
<span class="br0">}</span><span class="sy4">;</span>
 
<span class="kw1">namespace</span> std <span class="br0">{</span>
    <span class="kw1">template</span><span class="sy1">&lt;&gt;</span> <span class="kw1">struct</span> hash<span class="sy1">&lt;</span>Foo<span class="sy1">&gt;</span> <span class="br0">{</span>
        <a href="../../types/size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> operator<span class="br0">(</span><span class="br0">)</span><span class="br0">(</span><span class="kw4">const</span> Foo <span class="sy3">&amp;</span>f<span class="br0">)</span> <span class="kw4">const</span> <span class="br0">{</span>
            <span class="kw1">return</span> <a href="../../utility/hash.html"><span class="kw1124">std::<span class="me2">hash</span></span></a><span class="sy1">&lt;</span><span class="kw4">int</span><span class="sy1">&gt;</span><span class="br0">{</span><span class="br0">}</span><span class="br0">(</span>f.<span class="me1">val</span><span class="br0">)</span><span class="sy4">;</span>
        <span class="br0">}</span>  
    <span class="br0">}</span><span class="sy4">;</span>
<span class="br0">}</span>
 
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
<span class="br0">{</span>
    <span class="co1">// 默认构造函数：空 unordered_map</span>
    <a href="../unordered_map.html"><span class="kw1293">std::<span class="me2">unordered_map</span></span></a><span class="sy1">&lt;</span><a href="../../string/basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a>, <a href="../../string/basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a><span class="sy1">&gt;</span> m1<span class="sy4">;</span>
 
    <span class="co1">// 列表构造函数</span>
    <a href="../unordered_map.html"><span class="kw1293">std::<span class="me2">unordered_map</span></span></a><span class="sy1">&lt;</span><span class="kw4">int</span>, <a href="../../string/basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a><span class="sy1">&gt;</span> m2 <span class="sy1">=</span>
    <span class="br0">{</span>
        <span class="br0">{</span><span class="nu0">1</span>, <span class="st0">"foo"</span><span class="br0">}</span>,
        <span class="br0">{</span><span class="nu0">3</span>, <span class="st0">"bar"</span><span class="br0">}</span>,
        <span class="br0">{</span><span class="nu0">2</span>, <span class="st0">"baz"</span><span class="br0">}</span>,
    <span class="br0">}</span><span class="sy4">;</span>
 
    <span class="co1">// 复制构造函数</span>
    <a href="../unordered_map.html"><span class="kw1293">std::<span class="me2">unordered_map</span></span></a><span class="sy1">&lt;</span><span class="kw4">int</span>, <a href="../../string/basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a><span class="sy1">&gt;</span> m3 <span class="sy1">=</span> m2<span class="sy4">;</span>
 
    <span class="co1">// 移动构造函数</span>
    <a href="../unordered_map.html"><span class="kw1293">std::<span class="me2">unordered_map</span></span></a><span class="sy1">&lt;</span><span class="kw4">int</span>, <a href="../../string/basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a><span class="sy1">&gt;</span> m4 <span class="sy1">=</span> std<span class="sy4">::</span><span class="me2">move</span><span class="br0">(</span>m2<span class="br0">)</span><span class="sy4">;</span>
 
    <span class="co1">// 范围构造函数</span>
    <a href="../vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a><span class="sy1">&lt;</span><a href="../../utility/pair.html"><span class="kw1096">std::<span class="me2">pair</span></span></a><span class="sy1">&lt;</span><a href="../../utility/bitset.html"><span class="kw1027">std::<span class="me2">bitset</span></span></a><span class="sy1">&lt;</span><span class="nu0">8</span><span class="sy1">&gt;</span>, <span class="kw4">int</span><span class="sy1">&gt;&gt;</span> v <span class="sy1">=</span> <span class="br0">{</span> <span class="br0">{</span><span class="nu12">0x12</span>, <span class="nu0">1</span><span class="br0">}</span>, <span class="br0">{</span><span class="nu12">0x01</span>,<span class="sy2">-</span><span class="nu0">1</span><span class="br0">}</span> <span class="br0">}</span><span class="sy4">;</span>
    <a href="../unordered_map.html"><span class="kw1293">std::<span class="me2">unordered_map</span></span></a><span class="sy1">&lt;</span><a href="../../utility/bitset.html"><span class="kw1027">std::<span class="me2">bitset</span></span></a><span class="sy1">&lt;</span><span class="nu0">8</span><span class="sy1">&gt;</span>, <span class="kw4">double</span><span class="sy1">&gt;</span> m5<span class="br0">(</span>v.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span>, v.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span>
 
    <span class="co1">// 带定制 Key 类型的构造函数的选项 1</span>
    <span class="co1">// 定义 KeyHash 与 KeyEqual 结构体并在模板中使用它们</span>
    <a href="../unordered_map.html"><span class="kw1293">std::<span class="me2">unordered_map</span></span></a><span class="sy1">&lt;</span>Key, <a href="../../string/basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a>, KeyHash, KeyEqual<span class="sy1">&gt;</span> m6 <span class="sy1">=</span> <span class="br0">{</span>
            <span class="br0">{</span> <span class="br0">{</span><span class="st0">"John"</span>, <span class="st0">"Doe"</span><span class="br0">}</span>, <span class="st0">"example"</span><span class="br0">}</span>,
            <span class="br0">{</span> <span class="br0">{</span><span class="st0">"Mary"</span>, <span class="st0">"Sue"</span><span class="br0">}</span>, <span class="st0">"another"</span><span class="br0">}</span>
    <span class="br0">}</span><span class="sy4">;</span>
 
    <span class="co1">// 带定制 Key 类型的构造函数的选项 2</span>
    <span class="co1">// 为 class/struct 定义 const == 运算符并于 std 命名空间特化 std::hash 结构体</span>
    <a href="../unordered_map.html"><span class="kw1293">std::<span class="me2">unordered_map</span></span></a><span class="sy1">&lt;</span>Foo, <a href="../../string/basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a><span class="sy1">&gt;</span> m7 <span class="sy1">=</span> <span class="br0">{</span>
        <span class="br0">{</span> Foo<span class="br0">(</span><span class="nu0">1</span><span class="br0">)</span>, <span class="st0">"One"</span><span class="br0">}</span>, <span class="br0">{</span> <span class="nu0">2</span>, <span class="st0">"Two"</span><span class="br0">}</span>, <span class="br0">{</span> <span class="nu0">3</span>, <span class="st0">"Three"</span><span class="br0">}</span>
    <span class="br0">}</span><span class="sy4">;</span>
 
    <span class="co1">// 选项 3 ：用 lambdas</span>
    <span class="co1">// 注意必须将初始桶数传递给构造函数</span>
    <span class="kw1">struct</span> Goo <span class="br0">{</span><span class="kw4">int</span> val<span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
    <span class="kw4">auto</span> hash <span class="sy1">=</span> <span class="br0">[</span><span class="br0">]</span><span class="br0">(</span><span class="kw4">const</span> Goo <span class="sy3">&amp;</span>g<span class="br0">)</span><span class="br0">{</span> <span class="kw1">return</span> <a href="../../utility/hash.html"><span class="kw1124">std::<span class="me2">hash</span></span></a><span class="sy1">&lt;</span><span class="kw4">int</span><span class="sy1">&gt;</span><span class="br0">{</span><span class="br0">}</span><span class="br0">(</span>g.<span class="me1">val</span><span class="br0">)</span><span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
    <span class="kw4">auto</span> comp <span class="sy1">=</span> <span class="br0">[</span><span class="br0">]</span><span class="br0">(</span><span class="kw4">const</span> Goo <span class="sy3">&amp;</span>l, <span class="kw4">const</span> Goo <span class="sy3">&amp;</span>r<span class="br0">)</span><span class="br0">{</span> <span class="kw1">return</span> l.<span class="me1">val</span> <span class="sy1">==</span> r.<span class="me1">val</span><span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
    <a href="../unordered_map.html"><span class="kw1293">std::<span class="me2">unordered_map</span></span></a><span class="sy1">&lt;</span>Goo, <span class="kw4">double</span>, decltype<span class="br0">(</span>hash<span class="br0">)</span>, decltype<span class="br0">(</span>comp<span class="br0">)</span><span class="sy1">&gt;</span> m8<span class="br0">(</span><span class="nu0">10</span>, hash, comp<span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span></pre></div></div>
<p><br> 
</p>
</div>
<h3><span class="mw-headline" id=".E7.BC.BA.E9.99.B7.E6.8A.A5.E5.91.8A">缺陷报告</span></h3>
<p>下列更改行为的缺陷报告追溯地应用于以前出版的 C++ 标准。
</p>
<table class="dsctable" style="font-size:0.8em">
<tr>
<th> DR
</th>
<th> 应用于
</th>
<th> 出版时的行为
</th>
<th> 正确行为
</th></tr>
<tr>
<td> <a rel="nofollow" class="external text" href="https://cplusplus.github.io/LWG/issue2193">LWG 2193</a>
</td>
<td> C++11
</td>
<td> 默认构造函数为 explicit
</td>
<td> 使之为非 explicit
</td></tr></table>
<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
<table class="t-dsc-begin">

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="operator%3D.html" title="cpp/container/unordered map/operator="> <span class="t-lines"><span>operator=</span></span></a></div></div>
</td>
<td>   赋值给容器  <br> <span class="t-mark">(公开成员函数)</span> </td></tr>
</table>

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